Preprocessing
In this example, a 2D hash table H is used. It has a bin for each cell in the frame systems. In a preprocessing phase, the coordinates of all points in each model frame system are found. If there is a point in the cell (p,q) in the frame system with basis (ai,ak), then (ai,ak) is placed in the bin H(p,q)
Since all pairs of points from the model will (generally) act as basis pairs, totally pairs will be in H